U.S. patent number 6,331,586 [Application Number 09/248,277] was granted by the patent office on 2001-12-18 for conductive polymer blends with finely divided conductive material selectively localized in continuous polymer phase or continuous interface.
This patent grant is currently assigned to Cabot Corporation. Invention is credited to Alain Thielen, Baudouin Valange, Stefan Viering.
United States Patent |
6,331,586 |
Thielen , et al. |
December 18, 2001 |
Conductive polymer blends with finely divided conductive material
selectively localized in continuous polymer phase or continuous
interface
Abstract
A conductive polymer blend comprising: (a) at least two polymers
which are at least partially immiscible with each other, and are
present in proportions such that each polymer forms a respective
continuous phase and the two respective continuous polymer phases
are co-continuous with each other in the polymer blend; and (b) at
least one conductive material in particulate or fiber form which is
substantially localized in one of said co-continuous polymer phases
or substantially localized at a continuous interface between said
co-continuous polymer phases. Optionally, the polymer blend may
contain a mineral filler and/or a thixotropic thickening agent.
Inventors: |
Thielen; Alain (Thimister,
BE), Valange; Baudouin (Trooz, BE),
Viering; Stefan (Aachen, DE) |
Assignee: |
Cabot Corporation (Boston,
MA)
|
Family
ID: |
22119797 |
Appl.
No.: |
09/248,277 |
Filed: |
February 11, 1999 |
Current U.S.
Class: |
524/401; 524/430;
524/507; 524/525; 524/528 |
Current CPC
Class: |
C08L
23/06 (20130101); C08L 23/0815 (20130101); C08L
23/12 (20130101); H01B 1/20 (20130101); H01B
1/22 (20130101); H01B 1/24 (20130101); C08L
23/06 (20130101); C08L 23/06 (20130101); C08L
23/0815 (20130101); C08L 23/12 (20130101); C08L
23/16 (20130101); C08L 75/00 (20130101); C08L
2666/20 (20130101); C08L 2666/04 (20130101); C08L
2666/04 (20130101); C08L 2666/04 (20130101) |
Current International
Class: |
H01B
1/20 (20060101); H01B 1/24 (20060101); H01B
1/22 (20060101); C08K 003/00 (); C08L 083/00 ();
C08L 031/04 () |
Field of
Search: |
;524/507,528,525,430,401 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
0 486 307 A2 |
|
Nov 1991 |
|
EP |
|
0 971 366 A1 |
|
Jan 2000 |
|
EP |
|
0 971 368 A1 |
|
Jan 2000 |
|
EP |
|
94-206730 |
|
May 1994 |
|
JP |
|
Other References
Thesis from the Universite De Liege, Faculte des Sciences Etude de
Melanges Composites Polymeres Conducteurs de l'Electricite a Base
de Noir de Carbone pp. 1-203. (1995-1996). .
International Search Report for PCT/US99/02882, mailed Jun. 22,
1999..
|
Primary Examiner: Mulcahy; Peter D.
Parent Case Text
This application is a continuation-in-part of prior provisional
application Ser. No. 60/074,483 filed Feb. 12, 1998, which is
incorporated in its entirety by reference herein.
Claims
What is claimed is:
1. A conductive polymer blend comprising:
(a) at least two polymers which are at least partially immiscible
with each other, and are present in proportions such that each
polymer forms a respective continuous phase and the two respective
continuous polymer phases are co-continuous with each other in the
polymer blend; and
(b) at least one conductive material in particulate or fiber form
which is substantially localized in one of said co-continuous
polymer phases or substantially localized at a continuous interface
between said co-continuous polymer phases, wherein said at least
two polymers are a pair selected from the following pairs of
polymers:
HDPE/TPU
HDPE/EPR
HDPE/EPDM
HDPE/mLLDPE
PP/EPDM
PP/EPR
PP/mLLDPE
mLLDPE/EPR
2. A conductive polymer blend according to claim 1, wherein said
conductive material is a carbon product.
3. A conductive polymer blend according to claim 2, wherein said
carbon product is a carbon black.
4. A conductive polymer blend according to claim 1, wherein said
conductive material is at least one member selected from steel
fibers, metal powders or flakes, organic semiconductor powders,
metal-coated fibers, conductive metal oxide particles, or inorganic
particles coated with a conductive layer.
5. A conductive polymer blend according to claim 4, wherein said
conductive material is a powder of particles of TiO.sub.2 covered
with a layer of Sb.sub.2 O.sub.5 -doped SnO.sub.2.
6. A conductive polymer blend according to claim 5, wherein said
particles of TiO.sub.2 covered with a layer of 5b.sub.2 O.sub.5
doped SnO.sub.2 are acicular.
7. A conductive polymer blend according to claim 4, wherein said
conductive material has a particle size not greater than about 20
.mu.m.
8. A conductive polymer blend according to claim 1, wherein said
conductive polymer forms a product which retains at least about 65%
of the tensile strength at break of the polymer in the blend which
has the highest tensile strength at break, as compared to the other
polymers in the blend, if each polymer were used as a single-phase
polymer system and formed into a product under the same
conditions.
9. A conductive polymer blend according to claim 1, wherein said
conductive polymer forms a product which retains at least about 60%
of the resilience of the polymer in the blend which has the highest
resilience, as compared to the other polymers in the blend, if each
polymer were used as a single-phase polymer system and formed into
a product under the same conditions.
10. A conductive polymer blend according to claim 1, wherein said
conductive polymer forms a product which retains at least about 65%
of the tensile modulus of the polymer in the blend which has the
highest tensile modulus, as compared to the other polymers in the
blend, if each polymer were used as a single-phase polymer system
and formed into a product under the same conditions.
11. A conductive polymer blend according to claim 1, wherein said
conductive polymer forms a product which retains at least about 65%
of the elongation at break of the polymer in the blend which has
the highest elongation at break, as compared to the other polymers
in the blend, if each polymer were used as a single-phase polymer
system and formed into a product under the same conditions.
12. A conductive polymer blend comprising:
(a) at least two polymers which are at least partially immiscible
with each other, and are present in proportions such that each
polymer forms a respective continuous phase and the two respective
continuous polymer phases are co-continuous with each other in the
polymer blend;
(b) at least one conductive material in particulate or fiber form
which is substantially localized in one of said co-continuous
polymer phases or substantially localized at a continuous interface
between said co-continuous polymer phases; and
(c) at least one mineral filler.
13. A conductive polymer blend according to claim 12, wherein said
mineral filler is selected from inorganic carbonates, silicates,
aluminosilicates, oxides, hydroxides, sulfates, or sulfides.
14. A conductive polymer blend according to claim 12, wherein said
mineral filler is calcium carbonate, talc, or precipitated
silica.
15. A conductive polymer blend according to claim 12, wherein said
mineral filler has a particle size not greater than about 50
.mu.m.
16. A conductive polymer blend according to claim 12, wherein said
conductive polymer forms a product which retains at least about 65%
of the tensile strength at break of the polymer in the blend which
has the highest tensile strength at break, as compared to the other
polymers in the blend, if each polymer were used as a single-phase
polymer system and formed into a product under the same
conditions.
17. A conductive polymer blend according to claim 12, wherein said
conductive polymer forms a product which retains at least about 60%
of the resilience of the polymer in the blend which has the higher
resilience, as compared to the other polymers in the blend, if each
polymer were used as a single-phase polymer system and formed into
a product under the same conditions.
18. A conductive polymer blend according to claim 12, wherein said
conductive polymer forms a product which retains at least about 65%
of the tensile modulus of the polymer in the blend which has the
highest tensile modulus, as compared to the other polymers in the
blend, if each polymer were used as a single-phase polymer system
and formed into a product under the same conditions.
19. A conductive polymer blend according to claim 12, wherein said
conductive polymer forms a product which retains at least about 65%
of the elongation at break of the polymer in the blend which has
the highest elongation at break, as compared to the other polymers
in the blend, if each polymer were used as a single-phase polymer
system and formed into a product under the same conditions.
20. A conductive polymer blend according to claim 12, wherein said
at least two polymers are a pair selected from the following pairs
of polymers:
HDPE/TPU
HDPE/EPR
HDPE/EPDM
HDPE/mLLDPE
PP/EPDM
PP/EPR
PP/mLLDPE
mLLDPE/EPR,
21. A conductive polymer blend comprising:
(a) at least two polymers which are at least partially immiscible
with each other, and are present in proportions such that each
polymer forms a respective continuous phase and the two respective
continuous polymer phases are co-continuous with each other in the
polymer blend;
(b) at least one conductive material in particulate or fiber form
which is substantially localized in one of said co-continuous
polymer phases or substantially localized at a continuous interface
between said co-continuous polymer phases; and
(c) at least one thixotropic thickening agent.
22. A conductive polymer blend according to claim 21, wherein the
thixotropic thickening agent is fumed silica.
23. A method for preparing a conductive polymer blend, comprising
the steps of blending:
(a) at least two polymers which are at least partially immiscible
with each other, and are present in proportions such that each
polymer forms a respective continuous phase and the two respective
continuous polymer phases are co-continuous with each other in the
polymer blend; and
(b) at least one conductive material in particulate or fiber form
which is substantially localized in one of said co-continuous
polymer phases or substantially localized at a continuous interface
between said co-continuous polymer phases, wherein said at least
two polymers are a pair selected from the following pairs of
polymers:
HDPE/TPU
HDPE/EPR
HDPE/EPDM
HDPE/mLLDPE
PP/EPDM
PP/EPR
PP/mLLDPE
mLLDPE/EPR,
24. An article formed from a conductive polymer blend of claim
1.
25. An article formed from a conductive polymer blend of claim
12.
26. An article formed from a conductive polymer blend of claim
21.
27. An article according to claim 26, which is formed by blow
molding.
Description
BACKGROUND OF THE INVENTION
This invention relates to a polymeric material which is a
conductive blend of at least two polymers and contains at least one
finely divided conductive material. The invention also relates to
methods for preparing the conductive blends of polymers, and their
use.
Polymers in general are insulating materials. For certain
applications it is desirable for a polymeric material to have some
degree of electrical conductivity, for example in "ESD" or
electrostatic dissipative applications such as anti-static
packaging, housing for electronic equipment, containers and
pipelines for flammable liquids and gases, or in
charge-transporting components for electrographic imaging
equipment.
The addition of finely divided conductive material such as a
conductive carbon black is often used for achieving the desired
conductivity in a polymer or polymer blend. The conductive carbon
black is dispersed in the insulating polymer matrix. As the amount
of dispersed particles of carbon black is increased and reaches the
"percolation threshold" concentration, the particles come
sufficiently into contact with each other so that a marked increase
in conductivity is observed for the carbon black-loaded polymer.
The desired conductivity is obtained by controlling the loading of
the conductive particles such as carbon black. However, as the
concentration of carbon black increases, the mechanical properties
of the composite tend to deteriorate. The toughness and flexibility
of the composite decrease, and an article formed from the carbon
filled material is undesirably brittle.
In order to recover good impact strength and flexibility in
thermoplastic polymers containing carbon black, a common method
incorporates impact modifiers such as rubber particles, core/shell
acrylic copolymers, thermoplastic elastomers, or other reinforcing
agents into the thermoplastic composition. These additives increase
process complexity and generally cause other side effects such as
rheological modification or dispersion problems.
Another important detrimental effect of the presence of carbon
black in plastics is the reduction of the melt fluidity of the
thermoplastic polymers, which affects the ease of processability at
the transformer level (at the injection molder, extruder, blow
molder, thermoforming, etc.). A melt viscosity which is too high
can lead to a reduction of output rates, higher energy consumption,
increases in melt pressure and melt temperature, mold filling
problems, and polymer degradation.
In view of the above mentioned detrimental effects of the
incorporation of carbon black, it is desirable to reduce the amount
of carbon black in the polymer composition to improves its global
product property profile. For that reason, the carbon blacks used
are generally superconductive ones such as KETJENBLACK EC 600
JD.TM. (AKZO) or PRINTEX XE2.TM. (DEGUSSA) in order to obtain
electrical percolation at the minimum carbon black loading. It is,
however, generally difficult, if not impossible, to obtain
electrical conductivity for compositions containing, for example,
less than 5% KETJENBLACK EC 600 JD.TM., which is a highly
conductive carbon black.
Furthermore, although superconductive carbon blacks are generally
preferred to others due to the lower loading necessary to obtain a
percolation path, they present the worst structural characteristics
that can be envisioned with regards to the problems described
above. They are characterized by a high degree of structure (high
DBPA) and small primary particles (high surface area). As a
consequence, first, it is generally difficult to obtain good
dispersion of these carbon blacks in the composition (dispersion
being difficult for carbon black of small primary particle size),
which results in deficiencies in mechanical properties, and,
second, the viscosity of the obtained composition is high because
of the combination of a high degree of structure and a small
primary particle size. Consequently, even by using superconductive
carbon black, it is not possible to reduce the level of carbon
black sufficiently to overcome the problems described above.
More recently, another approach in reducing the carbon black
loading necessary for imparting conductivity to a polymer has been
investigated with specific blends of immiscible polymers which form
two co-continuous phases (i.e., two simultaneously and separately
continuous phases) in which the carbon black is localized
selectively in a continuous polymeric phase, or at the continuous
interface between the two co-continuous polymeric phases.
Investigations of the following polymer systems had thus been
reported:
HDPE/PS
PS/PMMA
PS/Rubbers (EPR, EPDM, polybutadiene, polyisoprene)
HDPE/ultrahigh molecular weight PE
PP/polyamide
PS/polyisoprene
PP/polycarbonate,
wherein PS = polystyrene PMMA = polymethyl methacrylate EPR =
ethylene propylene rubber EPDM = ethylene propylene diene rubber
HDPE = high density polyethylene PP = polypropylene.
In the above systems, under certain conditions the carbon black was
found to be selectively localized in one of the continuous
polymeric phases, or at the continuous interface between the
co-continuous polymeric phases. As a result of the selective
localization, conductivity was attained with a lower carbon black
load. In particular, when the carbon black was localized at the
continuous interface between the two co-continuous polymeric
phases, an even higher conductivity was obtained (i.e., the
percolation threshold concentration was greatly reduced) than when
the carbon black was localized in a continuous polymer phase.
However, the co-continuity of the blend which was required for
obtaining this reduction of the percolation threshold concentration
for electrical conductivity was not always achieved with all the
reported blends.
Although the mechanical properties of the above co-continuous
carbon black loaded-polymer blends are less impaired because the
carbon black loading is less than in a single phase polymer matrix,
the blending of two such polymers which are not fully miscible and
not fully compatible nevertheless results in poorer mechanical
properties of the blends, as compared to the mechanical properties
of the polymer component in the blend which has the most desirable
mechanical properties when used by itself (i.e., as a single phase,
one-polymer composition). The reason is that there is poor
interfacial adhesion at the phase boundary between the two
polymers, which presents weak points at which fractures can find
easy propagation paths.
SUMMARY OF THE INVENTION
An object of the invention is to provide conductive polymer blends
characterized by at least two co-continuous polymer phases
constituted by two polymers which are at least partially immiscible
with each other, in which the amount of finely divided conductive
material necessary to obtain electrical conductivity is lowered by
causing the finely divided conductive material to localize
substantially in a selective manner in a continuous polymer phase
in the blend, or at the continuous interface between the
co-continuous polymer phases, without significant deterioration of
the mechanical properties of the polymer blends.
Another object of the invention is to provide conductive polymer
blends which may be colored to any color.
Another object of the invention is to provide a conductive polymer
blend which is suitable for processing by any method, including
blow molding.
Yet another object of the invention is to provide a method for
preparing conductive polymer blends characterized by at least two
co-continuous polymer phases constituted by two polymers which are
at least partially immiscible with each other, wherein a finely
divided conductive material is substantially localized in a
selective manner in a continuous polymer phase or at the continuous
interface between two co-continuous polymer phases, and the
conductive polymer blends have improved mechanical properties.
Another object of the invention is to provide articles formed from
the co-continuous conductive polymer blends.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a graph showing the co-continuity domain of a polymer
blend of the invention.
FIG. 2 is a graph showing the co-continuity domain of another
polymer blend of the invention.
FIG. 3 is a TEM microphotograph of an embodiment of the conductive
co-continuous polymer blend of the invention.
FIG. 4 is a TEM microphotograph at a larger magnification of the
embodiment of the conductive co-continuous polymer blend shown in
FIG. 3.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to polymer compositions which contain
a finely divided conductive material, such as carbon black and/or
other carbon products, in a lower amount than conventionally used
to obtain acceptable electrical conductivity. By reducing the
amount of conductive material needed to obtain acceptable
electrical conductivity, other advantages can also be gained,
including the reduction or elimination of impact modifiers which
are generally needed when large amounts of carbon black are used,
substantially maintaining the melt viscosity of the polymeric
composition which existed prior to the introduction of the finely
divided conductive materials, and minimizing the carbon black
sloughing and rub off effect from a product made with the
composition. In specific polymer/carbon black combinations, the
selective localization of the carbon black allows the obtention of
very low percolation thresholds; far lower than those observed with
classical polymer systems filled with carbon black, even when using
carbon blacks which are not particularly designed for conductive
applications (i.e., carbon blacks having a larger particle size,
and less structure development).
Carbon blacks or other carbon powders or aggregates are preferred
as the finely divided conductive material for many applications of
the conductive polymer blend of the invention. While the preferred
carbon product is carbon black, any carbon product can be used that
is compatible with polymeric compositions. The carbon product may
be of the crystalline or amorphous type. Examples include, but are
not limited to, graphite, carbon black, vitreous carbon, activated
charcoal, activated carbon, carbon fibers, and mixtures thereof.
Mixtures or combinations of any of the carbon products can be used
as well.
The following grades are examples of carbon black suitable for use
in the conductive polymer blend of the invention:
KETJENBLACK EC600JD.TM. (AKZO)
KETJENBLACK EC300.TM. (AKZO)
PRINTEX XE2.TM. (DEGUSSA)
VULCAN P.TM. (CABOT CORPORATION)
VULCAN XC-72.TM. (CABOT CORPORATION)
UNITED 120.TM. (CABOT CORPORATION)
BLACK PEARLS 1000.TM. (CABOT CORPORATION)
ENSACO 250.TM. (MMM CARBON)
ENSACO 350.TM. (MMM CARBON)
DENKA BLACK.TM. (DENKA)
The finely divided conductive material may be other conductive
powders, fibers, aggregates or composite particles such as steel
fibers, metal powders or flakes (e.g., silver or aluminum flakes),
organic semiconductor powders, metal-coated fibers (e.g.,
nickel-coated fibers), conductive metal oxide particles (e.g.,
SnO.sub.2), inorganic particles coated with a conductive layer
(e.g., metal oxide particles such as TiO.sub.2 coated with Sb.sub.2
O.sub.5 -doped SnO.sub.2), etc. There is no particular limitation
on the finely divided conductive material, provided that it does
not react chemically with the components of the polymer blend, and
can be dispersed in a polymer phase in the blend, or be dispersed
at the interface between polymer phases in the blend. When the
finely divided conductive material is dispersed in a polymer phase,
it is preferable that the size of the conductive material be no
greater than the size of the phase of that polymer. At least, the
particle size of the conductive material should not be
substantially larger than the size of the phase of polymer in which
the conductive material is dispersed. In general, the particle size
of the conductive material is selected to be of a suitable size not
greater than about 20 .mu.m, preferably not greater than about 12
.mu.m, more preferably not greater than about 8 .mu.m, and even
more preferably not greater than about 6 .mu.m.
The finely divided conductive material is selected from materials
other than carbon black for applications requiring the polymer
blend to be colored to a color other than black. In general, the
color of these other finely divided conductive materials varies, in
particular from different shades of gray to white. Finely divided
conductive material which is light in color, such as particles of
TiO.sub.2 coated with Sb.sub.2 O.sub.5 -doped SnO.sub.2, which are
white, are suitable for preparing light-colored blends. In the case
of TiO.sub.2 coated with Sb.sub.2 O.sub.5 -doped SnO.sub.2 it is
particularly preferred that such conductive material be in the form
of acicular particles.
In combination with or in lieu of conventional carbon products,
modified carbon products can be used. For purposes of the present
invention, a modified carbon product includes an aggregate
comprising a carbon phase and a silicon-containing species phase. A
description of this aggregate as well as means of making this
aggregate are described in PCT Publication Nos. WO 96/37547 and WO
98/13418, U.S. Pat. Nos. 5,747,562; 5,622,557; and 5,830,930; as
well as U.S. patent application Nos. 08/528,895, now abandoned; and
08/750,017, now U.S. Pat. No. 6,028,137. All of these patents,
publications, and patent applications are hereby incorporated in
their entireties herein by reference.
The modified carbon product, for purposes of the present invention,
can also be an aggregate comprising a carbon phase and
metal-containing species phase where the metal-containing species
phase can contain a variety of different metals such as magnesium,
calcium, titanium, vanadium, cobalt, nickel, zirconium, tin,
antimony, chromium, neodymium, lead, tellurium, barium, cesium,
iron, molybdenum, aluminum, and zinc, and mixtures thereof. The
aggregate comprising the carbon phase and a metal-containing
species phase is described in U.S. patent application No.
08/828,785 filed Mar. 27, 1997, now U.S. Pat. No. 6,017,980 and PCT
Publication No. WO 98/42778 also hereby incorporated in its
entirety herein by reference.
Also, for purposes of the present invention, a modified carbon
product includes a silica-coated carbon black, such as that
described in PCT Publication Nos. WO 96/37547, and WO 98/13428,
also incorporated in their entireties herein by reference.
The modified carbon product can also be a carbon product or colored
pigment having attached at least one organic group which can
include a monomeric group, oligomeric group or polymeric group. The
organic group can be an aromatic group or an alkyl group. Examples
include those set forth in U.S. Pat. Nos. 5,672,198; 5,554,739;
5,571,311; 5,630,868; 5,707,432; 5,803,959; 5,698,016; 5,713,988;
and 5,851,280; and PCT Publication Nos. WO 96/18688; WO 97/47697;
and WO 97/47699, all incorporated in their entireties by reference
herein.
Furthermore, the modified carbon product can be a carbon product
having attached at least a stable free radical. Examples include
those described in U.S. patent application Nos. 08/962,244, now
abandoned; 08/968,299, now U.S. Pat. No. 6,068,688; and 09/181,926,
all incorporated in their entireties herein by reference.
The polymeric group can be any polymeric group capable of being
attached to a carbon product. The polymeric group can be a
polyolefin group, a polystyrenic group, a polyacrylate group, a
polyamide group, a polyester group, or mixtures thereof. Monomeric
groups are monomeric versions of the polymeric groups.
The organic group can also be an olefin group, a styrenic group, an
acrylate group, an amide group, an ester, or mixtures thereof. The
organic group can also be an aromatic group or an alkyl group,
either group with an olefin group, a styrenic group, an acrylate
group, an amide group, an ester group, or mixtures thereof, wherein
preferably the aromatic group, or the alkyl group, like a C.sub.1
-C.sub.12 group, is directly attached to the carbon product.
The polymeric group can include an aromatic group or an alkyl
group, like a C.sub.1 -C.sub.12 group, either group with a
polyolefin group, a polystyrenic group, a polyacrylate group, a
polyamide group, a polyester group, or mixtures thereof.
The organic group can also comprise an aralkyl group or alkylaryl
group, which is preferably directly attached to the carbon product.
Other examples of organic groups include a C.sub.1 -C.sub.100 alkyl
group.
The polymer blend is any composition having at least two
co-continuous polymer phases, in which the finely divided
conductive material can be dispersed in one polymer phase or at the
interface between the two co-continuous polymer phases. Polymeric
compositions as used in the present invention include thermoplastic
polymers and crosslinkable polymers or mixtures thereof.
Preferably, the polymeric composition contains at least one
thermoplastic polymer. The crosslinkable polymer usable in the
conductive blend of the invention includes rubbers and other
crosslinkable polymers or polymer blends.
The polymers in the conductive blend of the invention can be
homopolymers, copolymers, terpolymers, and/or polymers containing
any number of different repeating units. Further, the polymer can
be any type of polymer, such as a random polymer, alternating
polymer, grafted polymer, block polymer, star-like polymer and/or
comb-like polymer. The polymer can have the structure of an
interpenetrating polymer network, simultaneous interpenetrating
polymer network, or interpenetrating elastomeric network.
Specific examples of polymers include, but are not limited to,
linear high molecular weight polymers such as polyethylene,
poly(vinylchloride), polyisobutylene, polystyrene, polycaprolactam
(nylon), polyisoprene, and the like. Other general classes of
polymers include polyamides, polycarbonates, polyelectrolytes,
polyesters, polyethers, (polyhydroxy)benzenes, polyimides, polymers
containing sulfur (such as polysulfides, (polyphenylene) sulfide,
and polysulfones), polyolefins, polymethylbenzenes, polystyrene and
styrene copolymers (ABS included), acetal polymers, acrylic
polymers, acrylonitrile polymers and copolymers, polyolefins
containing halogen (such as polyvinyl chloride and polyvinylidene
chloride), fluoropolymers, ionomeric polymers, polymers containing
ketone group(s), liquid crystal polymers, polyamide-imides,
polymers containing olefinic double bond(s) (such as polybutadiene,
polydicyclopentadiene), polyolefin copolymers, polyphenylene
oxides, polyurethanes, thermoplastic elastomers and the like.
Generally, the polymers described in Volume 18 of the Encyclopedia
of Chemical Technology, KIRK-OTHMER, (1982), page 328 to page 887,
and Modern Plastics Encyclopedia '98, pages B-3 to B-210, both
incorporated in their entirety herein by reference, can be used as
the polymers in the present invention.
The polymers of the present invention can be prepared in a number
of ways and such ways are known to those skilled in the art. The
above referenced KIRK-OTHMER section and Modern Plastics
Encyclopedia provide methods by which these polymers can be
prepared.
In general, any pair of polymers may be selected for a blend
provided that the two polymers present at least some degree of
immiscibility and preferably differ in their polarity. Examples of
pairs of polymers suitable for use in this invention are:
- HDPE/TPU - PP/EPDM - HDPE/EPR - PP/EPR - HDPE/EPDM - PP/mLLDPE -
HDPE/mLLDPE - mLLDPE/EPR, wherein HDPE: high density polyethylene
TPU: thermoplastic urethane EPR: ethylene propylene rubber EPDM:
ethylene propylene diene rubber mLLDPE: metallocene catalyzed
linear low density polyethylene PP: polypropylene.
The above pairs of polymers are particularly suitable for use with
the specific grades of carbon black listed above.
The present invention makes it possible to use a smaller amount of
the finely divided conductive material in a polymeric composition
and yet obtain substantially the same, if not the same, electrical
conductivity as in the individual polymers loaded with the same
finely divided conductive material. In other words, in the present
invention substantially the same resistivity, if not the same, is
achieved with a lower amount of carbon black than is normally
required for achieving the same resistivity in the individual
polymers. This result is accomplished by using blends of polymers
having such characteristics that at least two co-continuous polymer
phases exist in the blend, and the finely divided conductive
material becomes substantially localized in a selective manner in
one of the co-continuous phases, or at the continuous interface
between two co-continuous polymer phases. At the same time, the
conductive polymer blend of the invention has acceptable mechanical
properties, notwithstanding the presence of the co-continuous,
immiscible polymer phases. The present invention thus avoids poor
internal adhesion, and consequently poor mechanical properties of
the polymer blend.
The polymer blend of the invention contains at least two polymers
which are immiscible, or at least partially immiscible, with each
other. The blend may contain other polymers in addition to the two
polymers which are at least partially immiscible with each other.
The additional polymer(s) does not have to be immiscible with any
of the other polymers in the blend. In other words, the additional
polymer(s) may be integrated into the continuous phase of another
polymer in the blend, or even be integrated simultaneously into two
or more separate continuous phases formed respectively by two or
more other polymers. Alternatively, the additional polymer(s) may
be immiscible with all other polymers in the blend, in which case
the additional polymer(s) may form its own continuous phase or be
dispersed inside the continuous phase formed by another polymer in
the blend.
Blends of immiscible polymers are characterized either by
morphologies wherein one of the polymers constitutes a dispersed
phase in a second polymer which is continuous, or by morphologies
where both polymer phases are co-continuous. In the latter case,
the interface between both polymer phases is also continuous in the
material. The conductive polymer blends of the invention contain at
least two co-continuous polymer phases in which each polymer phase
in effect forms a network, and the networks formed by the
individual polymer phases co-exist in the blend. The proportions of
the polymers constituting the blend are selected so that
co-continuity of the polymer phases is obtained. Each pair of
polymers is characterized by their co-continuity domain, which may
be different from the con-continuity domain of another pair of
polymers.
By selecting the nature of the polymers and the finely divided
conductive material, based on the specific interfacial interactions
between the finely divided conductive material and the polymers, it
is possible to localize selectively the finely divided conductive
material in a continuous polymeric phase or at the phase boundary,
that is, at the interface between two immiscible polymers which are
present as two co-existent continuous phases. In the case where the
conductive material has a preferred affinity with one of the
polymer phases, it will remain in that phase, or even migrate to
that phase if the viscosity of the polymer blend permits it and
there is no other impairment to the mobility of the conductive
material. In the case where the conductive material has no
particular affinity with any of the polymers, it will tend to
migrate to the interface in order to minimize the interfacial area
with both polymers. This situation will occur when the interfacial
tension of the conductive material is equally high with respect to
the various polymers of the blend. The interfacial tension between
two materials, such as between the conductive material and a
polymer, is calculated from the surface tension of the two
materials. This surface tension is composed of a dispersive
component and a polar component. In the conductive blend of the
invention, the polar component of the conductive material, which is
linked to its surface polarity, plays an important role in the
localization of the conductive material. That is, the polarity of
the conductive material, which relates to its surface oxidation and
can be measured by its pH, are important criteria in the
determination of the type of interaction between the conductive
material and a polymer. For example, in the HDPE/TPU system, a
carbon black with a pH which is neutral or above 8 becomes
essentially localized at the interface because it has no particular
affinity for any of the polymer phases. On the other hand, a carbon
black having a low pH, namely a carbon black which is highly
polar/oxidized, presents some affinity with TPU and becomes
localized in the TPU phase. In general, by selecting the type of
carbon product or pigment (for example, selecting the type of
modifying organic group attached to the carbon product or pigment),
it is possible to control the localization of the carbon product or
pigment in the co-continuous polymer blend.
To provide conductivity in the polymer blend, the aim is to build a
percolation path of the finely divided conductive material in the
material, either in the bulk of one continuous polymer phase or at
the interface between two polymer phases. As a result, electrical
conductivity is obtained at a loading of the finely divided
conductive material which is lower than the loading required for
obtaining conductivity in a single-phase polymer or polymer blend.
This lower loading required for obtaining the electrical
percolation should preserve the mechanical properties of the
polymers, which are generally negatively affected by the presence
of finely divided conductive material. It is preferred that the
finely divided conductive material be present in a sufficient
amount, which is at least equal to the percolation threshold
concentration for one or both of the polymer phases. However, the
loading of the finely divided conductive material should not be
excessively higher than the percolation threshold when stringent
control on the mechanical properties of a product formed from the
blend is necessary.
The conductive polymer blend of the invention may contain a mineral
filler. Examples of mineral fillers are inorganic compounds such as
carbonates, silicates, aluminosilicates, oxides, hydroxides,
sulfates or sulfides. Specific examples of a mineral filler are
calcium carbonate, talc, or precipitated silica. The particle size
of the mineral filler is not particularly limited, except that the
particle size is selected in view of the desired mechanical
strength. In general, it is preferred that the particle size of the
mineral filler be not greater than a "top cut" of about 50 .mu.m,
the top cut being the average particle size in 98% of the
particles. More preferably, the top cut of the mineral filler is
not greater than about 40 .mu.m. The mineral filler may have a
particle size in the same range as the finely divided conductive
material, or may be bigger than the finely divided conductive
material. When the particles of mineral filler are large, it is
believed that they may provide bridges between the different
polymer phases and thus reduce the tendency for the two immiscible,
non-compatible polymers to develop fractures at their boundaries.
On the other hand, the mineral filler may have a particle size
characterized by a top cut of no more than about 1 .mu.m. For
example, various CaCO.sub.3 having a top cut of about 2 .mu.m,
about 6 .mu.m, or about 12 .mu.m can be used in the conductive
polymer blend of the invention. The mineral filler may be of any
kind of particular shape, including granular, spherical, laminar,
flake-shaped, irregular and sharp, irregular and smooth, or
acicular forms. The amount of the mineral filler is selected
depending upon the desired balance between mechanical strength and
conductivity of the blend. In general, a mineral filler helps to
improve mechanical strength, but may impair conductivity if used in
large amounts. Conductive polymer blends having an acceptable
balance of properties have been obtained with up to about 10 wt. %
of mineral filler. In some instances, an even larger amount of up
to about 15 wt. %, and even about 20 wt. %, of mineral filler may
be used. A limiting factor, however, is that the mineral filler
should not be present in excess of the amount of the polymer phase
in which the mineral filler is distributed.
In addition to the polymers and the finely divided conductive
material, the polymer blend of the invention may also contain an
additive which functions as a thixotropic thickener in a non-polar
fluid. Examples of the thixotropic thickener are finely divided
silica known as "colloidal silica" or fumed silica, finely divided
alumina or bentonite, or mixtures thereof. The thixotropic
thickeners, such as fumed silica, are distinguished from the
mineral fillers described above, such as precipitated silica, by
their thixotropic effect on the melted polymer blend. Fumed silica
is a preferred thixotropic thickener for HDPE/TPU co-continuous
blends. In general, the amount of thixotropic thickener is less
than the amount of mineral filler used in the conductive polymer
blend according to the invention. The amount of thixotropic
thickener is selected to obtain the desired rheology of the melted
polymer blend according to the invention. In many instances, a
suitable amount of the thixotropic thickener is less than about 10
wt. %, more preferably less than about 5 wt. %, and even more
preferably less than about 2 wt. %.
The products made from the polymer blends of the invention are
characterized by a combination of strong mechanical properties with
enhanced electrical conductivity at a lower loading of the
conductive material, which is a combination not heretofore
achieved. In particular, the mechanical properties are fine-tuned
by appropriate selection of the constituent polymers, the finely
divided conductive material, the addition of mineral fillers or
thixotropic thickeners, as well as by the appropriate selection of
the proportions of the constituent polymers, the method of blending
the components of the polymer blend, the method of formation of the
polymer blend into a product, including the duration of annealing
treatment. The following factors are taken into consideration in
preparing a conductive polymer blend according to the present
invention:
Improved mechanical properties are achieved by selecting polymers
for blending which have similar physical properties so that
delamination of products prepared from the blend can be minimized.
It is acceptable that the polymers in the blend be only partially
immiscible. In other words, the two polymers may be partially
miscible, provided that the degree of miscibility does not destroy
the co-continuous blend morphology.
Within the co-continuity domain in a polymer blend, a ratio of the
two immiscible polymers is selected so that the polymer which has
the more desirable mechanical properties is present is a major
amount, as compared to the other polymer.
Two or more polymers which are miscible may be blended with each
other homogeneously to form a single phase having the desired
physical properties. For example, two polymers of different
flexibilities may be blended to obtain a blend having an
intermediate flexibility.
In general, the addition of a mineral filler helps to improve
mechanical strength of a product prepared from the polymer
blend.
For applications which require a smooth, flexible but strong
polymer melt, such as in blow molding applications, an additive
which functions as a thixotropic thickener in a non-polar fluid may
be added to improve the rheology of the polymer melt.
For applications requiring improved mechanical strength, annealing
a formed product generally results in improvement in the mechanical
strength, and may also improve the conductivity in the case where
the finely divided conductive material and/or the mineral filler is
in the form of elongated particles such as acicular particles, or
in the form of fibers.
The amount of shear stress applied to the material during the
mixing stage is carefully controlled in order to master the blend
morphology, which in turn determines the electrical and mechanical
properties of the composition. In general, a higher shear stress
causes a reduction in the size of each polymer phase. As the shear
stress is increased, the size of the phase of the polymer which is
present in a minority amount will decrease to the point where the
minority polymer is no longer in a continuous phase, but becomes
dispersed within the phase of the polymer which is present in a
greater amount, and the polymer blend loses its co-continuous
character.
The finely divided conductive material used to impart conductivity
to the composition is selected on the basis of its affinity/lack of
affinity with one or several polymer components of the blend, in
order to achieve accordingly a selective localization of this
conductive material in the blend.
By appropriate selection of the type of finely divided conductive
material and its amount, the natures of the polymers constituting
the respective co-continuous phases and their relative proportions,
the nature of the polymer blended into one of the co-continuous
phases (in the event a blend of polymers is used in that same phase
in lieu of a single polymer for the purpose of controlling the
properties of that phase as well as the properties of the overall
blend), the nature and amount of the optional mineral filler; the
nature and amount of the optional thixotropic thickening agent; the
thermoforming conditions, etc., as described above, a conductive
polymer blend may be obtained which retains at least about 60%,
preferably at least about 70%, and more preferably at least about
80%, of the resilience (as measured by the Izod impact strength,
for example) of the polymer in the blend which has the highest
resilience compared to the other polymers in the blend if each
polymer were used as a single-phase polymer system. Similarly, it
is possible to obtain a conductive polymer blend of the invention
which retains at least about 65%, preferably at least about 75%,
and more preferably at least about 85%, of the tensile strength at
break of the polymer in the blend which has the highest tensile
strength at break, as compared to the other polymers in the blend
if each polymer were used as a single-phase polymer system.
Also similarly, the conductive polymer blend of the invention may
be made to have at least about 65%, preferably at least about 75%,
and more preferably at least about 85%, of the tensile modulus of
the polymer in the blend which has the highest tensile modulus, as
compared to the other polymers in the blend if each polymer were
used as a single-phase polymer system. The conductive polymer blend
of the invention can also be prepared to have at least about 65%,
preferably at least about 75%, and more preferably at least about
85%, of the elongation at break of the polymer in the blend which
has the highest elongation at break, as compared to the other
polymers in the blend if each polymer were used as a single-phase
polymer system.
The conductive polymer blends of the invention can be compounded by
using common mixing equipment such as two-rotor mixers,
co-kneaders, twin-screw kneaders, Farrell continuous mixers (FCM),
long continuous mixers with axial discharge (LCM-AX), and the like.
In general, the finely divided conductive material may be
introduced directly into the polymer blend, or the finely divided
conductive material may be introduced into one of the polymers
before that polymer is blended with another polymer. In the case
where a crosslinkable polymer or polymer blend is used for one of
the continuous phases in the polymer, a crosslinking agent may be
added to the crosslinkable polymer or polymer blend before
compounding with the other components of the polymer blend of the
invention. The crosslinking agent is not particularly limited, and
can be any crosslinking agent specific to the polymer or polymer
blend to be croslinked. For example, a crosslinking agent for
rubber phases such as EPR and EPDM can be a sulfur-based curing
agent or a peroxide-based curing agent. For an example of a
non-rubber such as LDPE, organic peroxides are examples of suitable
crosslinking agents.
The conductive polymer blends of the invention are suitable for
forming into any product by any method, including injection
molding, compression molding, extrusion molding from a sheet, film
formation and blow molding.
A wide variety of articles may be produced from the polymer blends
of the invention, of which the following are non-limiting examples:
containers such as bottles, jerrycans, cartons, crates, boxes;
packaging; partitions; liners; pipes; pipelines; rods; tools or
components thereof; components for electronic equipment, including
housing and other parts such as charge transporting components in
electrographic imaging equipment.
Amongst others, very remarkable results that were observed with the
conductive polymer blends of the invention are:
Volume resistivities around 10.sup.3 ohm.cm and around 10.sup.5
ohm.cm were obtained with 1 wt % KETJENBLACK KEC600 JD.TM. and 1 wt
% PRINTEX XE2.TM., respectively, in HDPE/TPU systems ranging in
composition from 70/30 to 10/90. It should be noted that, in
general, more than 5 wt % KETJENBLACK KEC600 JD.TM. is necessary to
obtain such a level of conductivity in a single phase-polymer or
polymer blend.
In the 50/50 HDPE/TPU system, the percolation threshold has been
found to be around 0.35 wt % KETJENBLACK KEC600 JD.TM., which is an
extremely low value.
Similarly, 50/50 HDPE/TPU systems have been found to be conductive
(resistivity<5 10.sup.4 ohm.cm) when loaded with about 3 w %
VULCAN XC-72.TM., while more than 15 wt % of this carbon black is
usually required to obtain a low resistivity in a corresponding
single phase polymer or polymer blend.
Remarkably, UNITED 120.TM., which is a carbon black characterized
by a large particle size and is generally used for utility
pigmentation, not being at all designed for conductive application,
has been found to impart conductivity (resistivity around 10.sup.5
ohm.cm) to a 50/50 HDPE/TPU blend when present at only 15 wt %.
In the HDPE/TPU system which has a broad co-continuity range, it is
possible to select a blend with a ratio of polymers which gives the
desired mechanical properties (flexural, tensile and impact
properties) to a product formed from the blend.
PP/mLLDPE blends are particularly suitable for injection molding
applications, being characterized by a very high impact strength.
The mLLDPE (a metallocene catalyzed polyolefin) is characterized by
a narrow molecular weight, combined with a high average molecular
weight, which gives a very strong polymer. Therefore, PP/mLLDPE
blends have high impact strength even at the levels of conductive
material, e.g., carbon black, required for obtaining conductivity,
and even when the mLLDPE phase is saturated with carbon black.
These PP/mLLDPE blends also present the advantage that various
carbon blacks show very clear-cut affinities for one or the other
polymer phase, so that it is possible to design blends with the
desired properties by selection of the carbon to be localized
entirely in only one polymer phase. For example, ELFTEX 254.TM.
(CABOT CORPORATION) localizes entirely in the mLLDPE phase, whereas
ELFTEX 460.TM. (CABOT CORPORATION) localizes entirely in the PP
phase. Another advantage of the PP/mLLDPE system is that mLLDPE is
available in a broad range of properties depending on its density,
from rubber-like to being more like a classical thermoplastic PE.
Therefore, an appropriate grade of mLLDPE may be selected for the
desired application.
The HDPE/TPU system containing fumed silica as an additive is
particularly suitable for blow molding of containers. The
properties of the blend in its melted state are very suitable for
the blow molding operation. For a polymer blend to be suitable for
blow molding, the melted polymer blend must have a sufficiently
high viscosity for a self-supporting parison to be obtained, and at
the same time, the melted polymer blend must have sufficient
elasticity to withstand the blow molding process and expand under
blowing into the desired shape. The HDPE/TPU system containing
fumed silica has a very favorable high melt strength, and gives a
parison having strikingly good form stability. Consequently, it is
possible to form products having a long dimension, which is
generally not possible in blow-molding operations. Moreover, the
obtained product has excellent mechanical properties, so that the
blend is suitable for use in making containers which must meet
stringent performance standards, for example, containers for
gasoline or other flammable liquids.
The following examples further illustrate aspects of the invention
but do not limit the invention. Unless otherwise indicated, all
parts, percentages, ratios, etc. in the examples and the rest of
the specification are by weight.
EXAMPLE 1 PP/EPR BLENDS
50/50 blends of PP (FINAPROP 3660.TM., FINA Chemicals) and EPR
(VISTALON 2504.TM., EXXON) were mixed in a laboratory scale
Brabender mixer (50 cm.sup.3 chamber) at 200.degree. C. until
melting, before 1 wt. % of the carbon blacks listed below was added
and blended for 10 minutes after introduction of the carbon black.
Compression molded samples were produced from the Brabender batch
and molded at 200.degree. C. for 10 minutes. A microtome was used
to prepare thin slices for observation of the morphology of the
blend by microscopic (TEM) observation which revealed that all the
carbon blacks tested were selectively localized in the EPR (rubber)
phase. The blends were co-continuous.
PRINTEX XE2.TM. (DEGUSSA)
BLACK PEARLS 1000.TM. (CABOT CORPORATION)
VULCAN XC-72.TM. (CABOT CORPORATION)
KETJENBLACK EC600JD.TM. (AKZO)
VULCAN P.TM. (CABOT CORPORATION)
UNITED 120.TM. (CABOT CORPORATION)
DENKA BLACK.TM. (DENKA)
EXAMPLE 2 PP/EPDM BLENDS
50/50 blends of PP (FINAPROP 3660.TM. from FINA Chemicals) and EPDM
(VISTALON 2504.TM. from EXXON) were prepared in the same manner as
in Example 1 with the following carbon blacks:
PRINTEX XE2.TM. (DEGUSSA)
BLACK PEARL S 1000.TM. (CABOT CORPORATION).
The carbon blacks were found to be localized in the rubber phase
(EPDM), and the blends were co-continuous. The electrical
properties were tested for the samples by measuring the resistivity
by means of the four-probe method. The results are shown in Table
1.
TABLE 1 50/50 PP/EPDM Volume resistivity Surface Resistivity 1 w %
carbon black (ohm .multidot. cm) (ohm/sq) PRINTEX XE2 8 .times.
10.sup.4 2 .times. 10.sup.6 BP1000 2 .times. 10.sup.12 4 .times.
10.sup.13 Experimental conditions: 1 wt % of carbon black blending:
10 min. at 200.degree. C. molding: 10 min. at 200.degree. C.
The resistivities shown in the above table are lower than the
resistivities observed with the same loading in a single phase EPDM
composition. Thus, it can be seen that when the carbon black is
localized in the EPDM phase in the co-continuous PP/EPDM blend,
conductivity can be achieved with very low loading of carbon black
(1 wt %) compared to the loading required for obtaining
conductivity in a composition containing only a single EPDM
phase.
EXAMPLE 3 LOCALIZATION OF VARIOUS CARBON BLACKS IN HDPE/TPU
50/50 HDPE/TPU blends were prepared with various carbon blacks in
the same manner as in Example 1 except as indicated below.
Localization of the carbon black in the samples was observed by
TEM. The results are shown in Table 2 which also shows the pH of
each carbon black.
TABLE 2 Carbon black grade pH Localization BP1000 .TM. 2.5 TPU
BLACK PEARLS L .TM. 2.5 TPU + little interface REGAL 400 .TM. 2.5
TPU + interface XC-72 .TM. 6 Interface KETJENBLACK EC 600 .TM. 7
Interface XE2 .TM. 7 Interface DENKA BLACK .TM. 7.6 HDPE +
interface UNITED 120 .TM. 8.0 Interface VULCAN P .TM. 8.5 Interface
ENSACO 250 .TM. 9.1 Interface + TPU Experimental conditions: 1 wt %
of carbon black blending: 10 min. at 200.degree. C. molding: 10
min. at 200.degree. C.
It is evident from the above data that carbon black localization
depends on the pH of the carbon black. Carbon blacks with a low pH
(i.e., more polar carbon blacks) tend to localize in the TPU phase.
Carbon blacks with a higher pH tend to localize at the interface,
in some instances with some distribution in one of the polymer
phases.
EXAMPLE 4 CO-CONTINUITY DOMAINS IN HDPE/TPU BLENDS
HDPE/TPU blends were prepared in the same manner as in Example 1,
using various HDPE/TPU ratios, with and without KETJENBLACK KEC600
JD.TM. (3 wt %). The continuous fraction of TPU was evaluated by
weight measurement after extraction was conducted on the polymer
blends with THF (tetrahydrofuran), which is a selective solvent for
TPU. The amount of TPU extracted from the blend represents the
fraction of the entire TPU content in the blend which is in a
continuous phase and is thus extractable. This "continuous
fraction" is a measure of the continuity of the TPU phase. The
results are shown in FIG. 1, from which it is evident that the
co-continuity domain of the HDPE/TPU system (with or without carbon
black loading) extends from 40 to 90 wt % TPU in the blend.
Therefore, the HDPE/TPU system is a very versatile system suitable
for a wide range of applications requiring that the relative
amounts of TPU and HDPE be adjusted to achieve the mechanical
properties desired for specific applications.
The co-continuity domain of the HDPE/TPU system was also studied
with another carbon black, VULCAN XC-72.TM., loaded at 3 wt % or 8
wt %. The results are shown in FIG. 2 from which it is evident that
the co-continuity domain is similar to that observed with
KETJENBLACK KEC600 JD.TM.. However, some variations are noted due
to an increase in carbon black loading. As the amount of carbon
black is increased, the amount of TPU which could not be extracted
by THF increased. On the other hand, for blends having a high
content of HDPE (90% and 80%) the continuous fraction of TPU was
increased by the carbon black loading.
EXAMPLE 5 ELECTRICAL PROPERTIES OF HDPE/TPU BLENDS
50/50 blends of HDPE and TPU were prepared in the same manner as in
Example 1, with 1 wt % of various carbon blacks as shown in Table
3. The volume resistivity and surface resistivity of the samples
are also shown in Table 3, from which it is evident that the nature
of the carbon black affects the electrical properties of the blend.
This observation is contrary to reports in the prior art for other
polymer blends that when the carbon black is localized at the
interface, the intrinsic properties of the carbon black are not
expected to have significant effects on the electrical properties
of the blend.
TABLE 3 Volume resistivity Surface after 1 h molding resistivity
after 50/50 HDPE/TPU blends filled at 200.degree. C. 1 h molding at
with 1 wt % of carbon black (.OMEGA. .multidot. cm) 200.degree. C.
(.OMEGA./sq) KETJENBLACK 600 JD .TM. 4.13 .times. 10.sup.3 5.66
.times. 10.sup.4 (interface) PRINTEX XE2 .TM. (interface) 8.32
.times. 10.sup.4 2.36 .times. 10.sup.6 VULCAN P .TM. (interface)
5.04 .times. 10.sup.10 5.04 .times. 10.sup.10 UNITED 120 .TM.
(interface) 8.92 .times. 10.sup.11 2 .times. 10.sup.14 VULCAN XC-72
.TM. (interface) 6.47 .times. 10.sup.11 6.6 .times. 10.sup.14 DENKA
BLACK .TM. (interface + 1.87 .times. 10.sup.12 4.5 .times.
10.sup.13 HDPE) BP100 .TM. (TPU) 2.65 .times. 10.sup.12 4.13
.times. 10.sup.13
EXAMPLE 6 HDPE/TPU BLENDS WITH CaCO.sub.3 AND CARBON BLACK
Blends of HDPE and TPU were prepared in the same manner as in
Example 1, with or without the addition of carbon black and/or
CaCO.sub.3 as shown in Table 4. The electrical and mechanical
properties of samples prepared from the blends are also shown in
Table 4.
TABLE 4 Ex 6-1 Ex. 6-2 Ex. 6-3 TPU.sup.1 30.00 29.00 19.00
HDPE.sup.2 69.75 67.75 67.75 CaCO.sub.3.sup.3 0 0 10.00 Carbon
Black.sup.4 0 3.00 3.00 Antioxidant.sup.5 0.25 0.25 0.25 Average
Volume 1.00E + 13 2.76E + 04 3.93E + 04 Resistivity.sup.6 (.OMEGA.
.multidot. cm) Average Resilience.sup.7 1.13 1.24 2.53 (kJ/m.sup.2)
Flexural Behavior.sup.8 Smooth Very brittle Very flexible Hard to
break Degree of Delamination No delamination Slight
Delamination.sup.9 delamination .sup.1 ELASTOLLAN 1174D .TM. (BASF
- ELASTOGRAN) a polyether TPU, more rigid than other TPUs, but
still less rigid than HDPE. .sup.2 FINATHENE 3802FL POWDER .TM.
(FINA Chemicals), a HDPE more flexible than other HDPEs but still
more rigid than ELASTOLLAN 1174D .TM.. .sup.3 OMYACARB OG-2 .TM.
(OMYA). .sup.4 KETJENBLACK EC600JD (AKZO). .sup.5 IRG 1010 (CIBA
Specialty Chemicals). .sup.6 Measured on five compression molded
specimens for each formulation (cross-section of 4 .times. 15
mm.sup.2 and length of 25 mm) according to CABOT D007A method. The
low resistivities were measured at 5 V and the higher at 500 V with
a Keithley 487 picoammeter. Five values of each sample were taken
after one minute electrification time. The results are expressed in
exponential format (e.g., 1.00E + 13 is the same as 1.00 .times.
10.sup.13). .sup.7 IZOD impact test made on six bars cut from
compression molded plaques and notched (dimensions 63.5 .times.
12.7 .times. 4 mm.sup.3 /Norm ISO 180/1A). Before the test the
specimens were stored under normal conditions at 23.degree. C. and
50% relative humidity. .sup.8 Manual evaluation folding test on 2
mm thick pressed plaques (10 .times. 10 cm.sup.2). .sup.9
Delamination = plaque broke after delamination.
The above results show that CaCO.sub.3 is able to replace some TPU
without impairing the conductivity of the polymer blend. The volume
resistivity of compression molded samples is not affected by
CaCO.sub.3. However, the volume resistivity of extruded tapes is
increased from 1 to 2 orders of magnitude. On the other hand, the
presence of CaCO.sub.3 is beneficial because of improvements in
strength of the blend.
EXAMPLE 7 HDPE/TPU WITH FUMED SILICA AND CARBON BLACK
30/70 TPU/HDPE blends (wherein the TPU portion was made up of 2
parts of rigid polyether PTU and 1 part of rigid polyester TPU and
the HDPE was of the rigid type) were prepared with and without the
addition of fumed silica as shown in Table 5. Pressed plaques
(Dimensions: 10.times.10 cm.sup.2 were formed by pressing at
200.degree. C. and 300 kN after 60 second-annealing. The electrical
and mechanical properties of the blends are also shown in Table
5.
TABLE 5 Ex. 7-1 Ex. 7-2 Ex. 7-3 ELASTOLLAN 1174D .TM..sup.1 19.4
19.3 19.0 (rigid polyether TPU) ELASTOLLAN C74D .TM..sup.1 9.7 9.6
9.5 (rigid polyester TPU) FINATHENE 3802 FL .TM..sup.1 67.8 67.4
66.6 (rigid HDPE) KETJENBLACK EC 6000 2.9 2.9 2.9 JD .TM..sup.3
CAB-O-SIL M5 .TM..sup.4 -0- 0.6 1.7 IRG. 1010 .TM.
(antioxidant).sup.5 0.2 0.2 0.2 Surface Resistivity
(.OMEGA./sq).sup.6 19.0E + 3 5.4E + 3 24.0E + 3 Young's Modulus
(MPa).sup.7 404 433 420 Stress @ yield(Mpa).sup.8 20.3 21.4 22.3
Folding Test.sup.9 Flexible Brittle/ Brittle/Surface Strong breaks
.sup.1 (ELASTOGRAN - BASF). .sup.2 (FINA Chemicals). .sup.3 (AKZO).
.sup.4 (CABOT CORPORATION), fumed silica premixed with TPU before
blending with HDPE, 4 minutes @ 220.degree. C. for each mixing
stage. .sup.5 (CIBA Specialty). .sup.6 Measured on pressed plaques
using two electrodes (25 mm long, 2 mm apart) according to DIN
53482, with two values taken for each sample. .sup.7 Measured
ACCORDING TO ISO R527, Type 2 specimens. .sup.8 Measured ACCORDING
TO ISO R527, Type 2 specimens. .sup.9 Manual evaluation folding
test on 2 mm thick pressed plaques (10 .times. 10 cm.sup.2).
The above examples show that the addition of fumed silica in an
appropriate amount helps to achieve a balance of tensile and
flexural characteristics without affecting to any significant
degree the resistivity of the polymer blend of the invention. The
70/30 HDPE/TPU blend having 0.6 wt % fumed silica added thereto
(Ex. 7-2) displayed a balance of flexural and tensile behaviors
which makes the blend suitable for blow molding into containers. A
TEM microphotograph of the blend of Ex. 7-2 is shown in FIG. 3, and
also in FIG. 4 at a larger magnification, on the scales indicated
in the respective microphotographs. The shaded background in the
microphotographs represents the HDPE phase. The lighter areas
represent the TPU phase, on which the smaller carbon black
particles are clearly visible.
Bottles (0.7 liter) were blow-molded on a KRUPP KAUTEX line (KEB
401, L=50; L/D=20, standard three-zone screw). The process was
controlled to give a laminar melt flow. The blow molding operation
showed good parison stability, with the polymer blend having 0.6 wt
% of fumed silica exhibiting greater stability than the polymer
blend having no fumed silica. In comparison, at a mass temperature
above 220.degree. C. the melt of the polymer blend having no fumed
silica became unstable.
EXAMPLE 8 PE/TPU WITH TiO.sub.2 COATED WITH Sb.sub.2 O.sub.5 -DOPED
SnO.sub.2
PE/TPU blends were prepared in the proportions shown in Table 6 by
mixing for 1 minute at low rotor speed in the chamber of a
Brabender mixer heated at 180.degree. C. After melting of the
polymers, particles of TiO.sub.2 covered with a layer of Sb.sub.2
O.sub.5 -doped SnO.sub.2 (FT-2000.TM. from ISHIHARA SANGYO KAISHA)
were introduced and mixed for 1 minute, and the rotor speed was
then increased to 65 rpm for 8 minutes. Pressed plaques
(10.times.10 cm.sup.2 were prepared by pressing at 180.degree.
C./50 kN for 10 minutes. The resistivity and the TPU phase
continuity were measured. The results are also shown in Table
6.
TABLE 6 Ex. 8-1 Ex. 8-2 Ex. 8-3 mLLDPE.sup.1 100 90 80 TPU.sup.2 0
10 20 FT-2000 (coated TiO.sub.2) 20 20 20 Volume Resistivity.sup.3
(.OMEGA. .multidot. cm) 8.0E + 12 1.3E + 4 6.5E + 6 TPU phase
continuity.sup.4 (%) N/A 100 96 .sup.1 Metallocene catalyzed LLDPE
(EXCEED 109), MFI(190.degree. C./2.16 kg) = 3 g/10 min, EXXON.
.sup.2 ESTANNE 58300 .TM. (B F Goodrich), polyether TPU. .sup.3
Measured on five compression molded specimens for each formulation
(cross-section of 4 .times. 15 mm.sup.2 and length of 25 mm)
according to CABOT D007A method. The low resistivities were
measured at 5 V and the higher at 500 V with a Keithley 487
picoammeter. Five values of each sample were taken after one minute
electrification time. The results are expressed in exponential
format (e.g., 1.00E + 13 is the same as 1.00 .times. 10.sup.13).
.sup.4 Measured by extraction of TPU phase with THF.
The above results show that the addition of TiO.sub.2 covered with
a layer of Sb.sub.2 O.sub.5 -doped SnO.sub.2 helped to reduce the
resistivity of the PE composition by up to 9 orders of magnitude
when 10 parts of TPU were blended with 90 parts of mLLDPE. As the
amount of TPU was increased to 20 parts, the TPU phase continuity
was decreased and the resistivity increased, even through the
resistivity was still about 6 orders of magnitude lower than when
no TPU was used in the composition.
Other embodiments of the present invention will be apparent to
those skilled in the art from consideration of the specification
and practice of the invention disclosed herein. It is intended that
the specification and examples be considered as exemplary only,
with a true scope and spirit of the invention being indicated by
the following claims.
* * * * *